The invention relates to a method for the manufacture of a bituminous coating sheet wherein a bitumen-impregnated and bitumen-coated core material is advanced across one or more rotating bodies during the manufacturing process. The invention also relates to an apparatus for exercising the method and a coating sheet produced by said method.
Such coating sheets are used eg for the coating of roofs. The coating sheet is generally configured with a core material that consists eg of woven or non-woven synthetic fibre. Usually, the core material is impregnated with bitumen and on the one or first face it is coated with a bituminous material wherein eg crushed slate is usually incorporated to increase the resistance of said coating sheet to eg sunlight. This side constitutes the outwardly facing, free side of the coating sheet. On the other side of the core material which is opposite the slate material, a bituminous coating is also provided, viz a so-called welding bitumen. Such coating sheets are often used in connection with the coating of eg bridges and the establishment of diffusion-proof underground membranes, eg in waste disposal areas, liquid manure containers, and the like.
In a known method of manufacturing a bituminous coating sheet, a core material impregnated with or coated with a bituminous material on the above-mentioned second side is strewn with a layer of sand that prevents, during the further manufacturing process, this side of the coating sheet from adhering to the rotating bodies that convey the coating sheet. In a concluding step of the manufacturing process, a bituminous material is added on top of the sand layerxe2x80x94preferably a so-called welding bitumen that serves to connect the coating sheet with a support on the site of use. However, the use of a sand layer as an anti-adhesion measure in connection with the manufacturing process is associated with the drawback that the subsequently applied welding bitumen can exhibit poor adhesive properties towards the remaining coating sheet. Thus, in connection with eg roof coverings, bridge coverings and the like membrane coatings, powerful external influences such as wind influences that cause a suction in the surface may cause delamination of the bituminous coating sheet. The consequence of such delaminations can be leakages with ensuing damage to the roof structure and/or the remaining part of the building or the plant.
Moreover, the sand layer involves a significant increase in the volume of the coating sheet.
It is an object of the invention to provide a method for the manufacture of such bituminous coating sheet wherein the finished product processes considerably increased delamination strength and a reduced volume compared to the prior art. Moreover, it is an object of the invention to provide an apparatus for exercising this method. Finally, it is an object of the invention to provide a coating sheet that possesses a considerably increased delamination strength compared to the prior art coating sheets.
According to the invention the method for the manufacture of such bituminous coating sheet is characterized in that a slip material being dispersed/emulsified or dissolved in a liquid is applied onto that side of the bituminous backface layer that is to be brought into contact with a rotating body; that the liquid is evaporated prior to contact with the rotating bodies for advancing the coating sheet; and
that subsequently a further bituminous layer is applied onto that side which is provided with the slip material.
By such method, even and thin application of the slip material is accomplished, and furthermore it enables use of slip materials having considerably increased adhesive properties compared to sand as known from the prior art. Finally, the option of applying the layer very thinly also enables a coating sheet with a considerably reduced volume, the layer thickness being otherwise unchanged as regards core and bitumen coatings.
According to a particularly convenient embodiment of the method, the dispersion/emulsion or the solution as the case may be is applied by a spraying process. This method enables safe control of the process and thereby ensures that the thinnest possible layer of slip material can be applied. Moreover, it will also be possible to accomplish the application by means of an anti set-off roller.
The dispersion/emulsion/solution is preferably applied onto the coating sheet at such distance from the first rotating body that said liquid is completely evaporated prior to contact with the first rotating body whereby is provided a solid, non-adhesive surface layer consisting of the slip material. In that context it is important thatxe2x80x94during application of the liquid slip materialxe2x80x94the bituminous material has a suitable temperature. Conveniently it is ranging from 100 to 200xc2x0 C., preferably, however, from 120 to 160xc2x0 C. The relatively elevated temperature permits quick evaporation of the liquid contents of the dispersion/emulsion or the solution, thereby accomplishing an advantageous cooling of the bituminous coating sheet that increases the viscosity of the bitumen material. Optionally further coolant can be supplied to the surface of the bitumen layer.
In the method, a polymer dispersion/emulsion is preferably used, eg a dispersion/emulsion of a thermoplastic polymer, eg acrylic-based or PVB (Polyvinyl Butyral) that can be admixed with a plasticizer. Alternatively a solution of polyvinylalcohol can be used.
An apparatus for exercising the method described above comprises rotating bodies for conveyance of the coating sheet and means for applying a dispersion/emulsion/solution of a slip material. Such means for applying the liquid slip material are conveniently in the form of one or more nozzles to which the dispersion/emulsion/solution is supplied under pressure. The pressurized supply can be accomplished by means of usual liquid pumps. Such embodiment with nozzles ensures the most homogenous distribution and thus the option of applying the thinnest possible layers of the slip material. These means for applying the liquid slip material are preferably arranged at such distance from the first rotating body that the liquid contents of the dispersion/emulsion/solution has evaporated completely prior to contact with the rotating body. It is a further option to provide an anti-set off roller for use in the application of the dispersion/emulsion/solution.
The invention also relates to a coating sheet which is characterised in comprising a core material, the one side of this core material being provided with a layer of a polymer-based slip material and adjacently this polymer-based slip material a bituminous layer. This is preferably a thermoplastic polymer.
Compared to the prior art coating sheets, such coating sheet has a considerablyincreased delamination strength and also has a considerably smaller volume than prior art coating sheets while maintaining as such the layer thicknesses of core and bitumen coatings.